1. Field of the Invention
The present invention relates generally to the field of lower extremity exoskeletons and, more particularly, to the field of lower extremity exoskeletons that decrease their wearer's energy consumption.
2. Discussion of the Prior Art
In a wide variety of situations, people of ordinary ability often consume a great deal of energy when walking or carrying a load. One attempt to improve load carrying ability is set forth in the paper entitled “A QUASI-PASSIVE LEG EXOSKELETON FOR LOAD-CARRYING AUGMENTATION”, C. J. Walsh, K. Endo, and H. Herr, International Journal of Humanoid Robotics, 2007. However, the quasi-passive exoskeleton taught by Walsh et al. increases its wearer's oxygen consumption. More specifically, the exoskeleton described has no actuation and power unit and therefore will not be able to transfer power from the exoskeleton to the person. This means that this type of system, regardless of the location and strength of its springs, will not decrease its wearer's energy expenditure. Since oxygen consumption is proportional to energy expended, a wearer's oxygen consumption will not be decreased.
An article published by Popular Science Magazine (May 2008) describes a powered exoskeleton system designed and built by Sarcos, that is controlled by a method called “get out of the way”. This method measures the forces and torques a wearer exerts onto the exoskeleton and drives the exoskeleton based on these measurements. This “get out of the way” control method has been extensively used in control of intelligent assist devices. See U.S. Pat. Nos. 6,299,139, 6,386,513, and 6,886,812. However, the “get out of the way” control method will not reduce a wearer's energy expenditure because the force from the exoskeleton onto the wearer is in the opposite direction to the wearer's motion and in fact increases the wearer's energy expenditure.
Based on the above, opportunities exist to provide a general purpose exoskeleton device that will decrease the wearer's energy consumption while the device is worn. Providing an exoskeleton that decreases the energy consumption of its wearer would allow a wearer to walk and carry heavy objects, while reducing the wearer's energy expenditure. In particular, this invention covers various embodiments of exoskeleton devices that decrease their wearers' energy expenditure during a stance phase.